Letter Case Permutation LeetCode solution in JavaScript

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const sliceRemaining = (s) => s.slice(1, s.length);
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var letterCasePermutation = function (s) {
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  let output = [];
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  const backtracking = (current, remaining) => {
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    if (!remaining.length) return output.push(current);
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    if (/^[0-9]+$/i.test(remaining[0])) {
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      current += remaining[0];
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      backtracking(current, sliceRemaining(remaining));
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    } else {
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      backtracking(
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        current + remaining[0].toLowerCase(),
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        sliceRemaining(remaining)
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      );
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      backtracking(
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        current + remaining[0].toUpperCase(),
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        sliceRemaining(remaining)
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      );
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    }
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  };
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  backtracking("", s);
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  return output;
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};